The electric guitar is an instrument with a very wide musical vocabulary. A large part of the electric guitar musical versatility derives from the varying sonic characteristics that may be provided by modern amplification. Unlike the piano, which also can play a wide variety of musical styles, yet always retains the same timbre for each style, the sound of the electric guitar emanates solely from the amplifier and its associated loudspeaker. Moreover, the guitar amplifier is no longer expected to operate exclusively in the linear domain, faithfully reproducing the original “acoustic” sound of the plucked strings.
Instead, the role of the modern guitar amplifier has expanded to include saturation distortion, an expressive sonic enhancement that is so vital to certain popular musical styles that they could not otherwise be created. In fact, some musical styles have arisen after the fact, in response to, and as a result of a particular amplifier's characteristics of sound distortion.
As examples, there is simply no way that searing, sustaining, single-note lead lines could have been played without a major dose of amplifier saturation. Over time, as amplifier over-drive characteristics became more extreme, the musical styles they spawned have become increasingly aggressive as illustrated by the entire genre of “heavy metal” and its various stylistic subsets, many of which are closely, if not nearly exclusively, the domain of certain models and settings of amplifiers and their distortion tonalities.
The origin of the modern distortion-enhancement amplifier dates to the “dual mode” circuit described in U.S. Pat. No. 4,211,893 of Randall C. Smith which provides a “lead mode” as well as the traditional “rhythm mode”, each being pre-settable and foot-switch selectable. In this design, extra stages of pre-amplification are cascaded such that massive overdrive saturation creates distortion that can go far beyond merely mimicking the sound of an amplifier “turned up too loud”.
However, the sound of a good vacuum tube amplifier “turned up too loud” must be acknowledged as the historical source of musical distortion for electric guitar. First used by blues players (who set the stage for the rock and rollers that followed), power amplifier distortion became a powerfully expressive tool.
The fundamental limitation of power amplifier distortion is its inseparable relation to amplifier loudness. Indeed, the distortion occurs only when, and as a result of, the amplifier being “turned up too loud”. One of the benefits of the amplifier of the above noted patent was its ability to separate playing loudness from distortion characteristics and this was accomplished by providing for massive, controllable saturation generated within the preamplifier, then providing user attenuation of the signal amplitude before coupling it to the power section. Though this approach can mimic power amplifier distortion (and more), it is not truly the same thing and differs in many respects.
First, unlike preamplifiers, power amplifiers are nearly all audio amplifiers are push-pull amplifiers. Second, power amplifiers almost all utilize pentode or beam power tubes, compared to the small triodes of the preamplifier. Third, power amplifiers couple through an output transformer to the loudspeaker. Fourth, there will always remain an abiding opinion that power amplifier distortion is more “legitimate” than preamplifier distortion, due to its historical roots.
Thus, despite the versatility provided by preamplifier distortion, there remains a strong need for providing authentic power amplifier distortion while remedying the age-old limitations presented by its link to playing loudness.